The present invention relates generally to analog-digital converters, and more particularly to an analog-digital converter for converting analog measurement signals into corresponding digital signals.
A circuit for converting a plurality of analog electrical measurement signals applied to input terminals into corresponding digital signals has become known, within the scope of the Siemens high-voltage protection unit 7 SA 502. In this unit, several analog electrical measurement signals are acquired by the circuit and, after being converted into digital signals, are compared to one another to determine faulty system conditions.
For this purpose, the circuit includes an antialiasing filter 1 (shown in FIG. 1) on the input side for each electrical measurement signal to be convened. It is linked by its input to an input terminal E1 to an analog electrical measurement signal M1. Altogether, twelve analog electrical measurement signals M1 through M12, which are each applied to input terminals E1 through E12, are acquired by the circuit. Since the input sections of the unit arranged downstream from the input terminals have the same design, only the input section for the analog electrical measuring signal M1 will be described in the following. An amplifier 2 having a gain of V=1 is arranged downstream from the antialiasing filter 1 just mentioned above. Linked to this amplifier 2 is a sample-and-hold circuit 3, which with one input 4 is arranged downstream from a multiplexer 5. An analog-digital converter 6 having a downstream evaluation unit (not shown in FIG. 1) connected to it, is linked to the multiplexer 5 on the output side.
Also depicted in FIG. 1 is another amplifier 7 having a gain of V=16, which is arranged downstream from the antialiasing filter 1. An additional multiplexer 9 having a further downstream analog-digital converter 10 connected to it on the output side is linked via an additional sample-and-hold circuit 8 to the other amplifier 7. This analog-digital converter 10 is likewise connected on the output side to the evaluation unit that is not shown. Provision is made to utilize the evaluation path comprising the amplifier 2, so that one will still be able to work with adequate precision, even given saturation of the amplifier 7.
In the same way as they are connected to the input terminal E1, the multiplexers 5 and 9 are connected via additional sample-and-hold circuits (not shown) corresponding to the circuits 3 and 8 as well as via amplifiers (likewise not shown) corresponding to the amplifiers 2 and 7, as well as in each case via an antialiasing filter corresponding to the filter 1 to the other input terminals for the measurable quantities M2 through M12.
The application of the sample-and-hold circuits 3 and 8 for the various analog electrical measuring signals M1 through M12 ensures that the various analog electrical measuring signals are each acquired at the same instant. After the query has been made by the multiplexers 5 and 9 and conversion into digital signals is complete, the state of the power system to be monitored can then be inferred in the evaluation device (not shown) from a comparison of the digital signals corresponding to the analog electrical measuring signals.
A circuit similar to the one shown in FIG. 1 is described in the "IBM Technical Disclosure Bulletin", vol. 33, no. 9, February 1981, pp. 4210-4213. Moreover, this literature reference discloses a circuit for converting a plurality of analog measuring signals being applied to input terminals into corresponding digital signals, in the case of which several measurable quantities are supplied to each of several multiplexers via input filters. On the output side, a series circuit comprising a sample-and-hold circuit having a downstream analog-digital converter is linked to each multiplexer.
Furthermore, EP 0 372 526 A2 discloses a microcomputer, which renders possible a rapid analog-digital conversion. In the case of this known arrangement, several sample-and-hold circuits are either linked to a single measurable quantity or to several measurable quantities via transfer gate circuits, which function as multiplexers due to their drive circuit. The sampled values are supplied one after another to a device for analog-digital conversion.
The present invention is directed to the problem of developing a circuit for converting a plurality of analog electrical measurement signals applied to input terminals into corresponding digital signals, which, while enhancing the effect of the antialiasing filter, can be realized with a relatively small number of circuit elements.